Integrated Underreamer Technology with Real-Time Communication Helped Eliminate Rathole in Exploratory Operation Offshore Nigeria

Abstract This paper describes the successful deployment of integrated underreamer technology with real-time communication through mud-pulse telemetry system, to drill and eliminate rathole in 17 1/2-in × 20-in successfully in one run and helped set casing as close as possible to the depth of suspected pressure ramp on an exploratory well offshore Nigeria. This technology uses the same communication system (actuator bypass) as Measurement While Drilling tools (MWD),Logging While Drilling tools (LWD) and Rotary Steerable System (RSS). Integrated underreamers broadly used in the drilling operations support optimized casing and completion programs and helps reduce operational risks such as wellbore instability. The ball drop and hydraulically activated reamer technologies available today comes with limitations and HSE risks. The distinctive functionalities of the integrated underreamer technology described here, such as unlimited and fast activation and deactivation via downlinking and real time downhole feedback,reduce uncertainties and operational costs in the complex and challenging deep offshore drilling operations. The real-time communication through mud-pulse telemetry system enabled the placement of integrated underreamer 6 meters from the bit thereby reducing rathole length to approximately 9 meters compared to 80 meters for conventional underreamer application. The integrated underreamer is compatible with existing RSS and provide unlimited activation cycles. The integrated underreamer offers flexibility in placement in the bottom hole assembly (BHA) and it can be used as a near bit reamer, or as main reamer or as both.In this case,the integrated near bit underreamer eliminated the need for a dedicated rathole removal run.It also offered a feedback confirmation of the cutter blades activation status and provided hole opening log thereby reducing the operational uncertainties for the under reaming, saving rig time up to 16 hours for shoulder test. The underreamer was successfully deployed to drill and ream the challenging 14 ¾’’ × 17 ½’’ and ream 17 ½’’ × 20’’ section offshore Nigeria. Both sections were drilled and reamed to section Total Depth (TD) in one run with all directional requirements and Measurement While Drilling (MWD)/Logging While Drilling (LWD) met,saving client approximately 4 days of rig spread cost. The reamer appeared to provide an in-gauge borehole allowing for successful running and cementing of liners without any issues, demonstrating superior borehole quality.The new Technology proved to be a reliable and flexible hole enlargement while drilling solution that help to improve drilling performance, reduce operational risks and save cost.